A choke is a small constriction located near the muzzle of a shotgun barrel that changes the patterning characteristics of a shot charge. Chokes have been used in firearms, and in particular shotguns, for many years to impact the percentage of pellets that will hit a target at a fixed distance from the muzzle. While some gun barrels have fixed chokes, removable choke tubes are preferred by many users.
Removable chokes permit one shotgun to be used for a variety of shooting applications. For example, very tight, i.e., small exit diameter, chokes are used to maintain a high percentage of the shot charge in a tight pattern at a long distance from the muzzle of the shotgun. This characteristic is desirable for long-range shooting situations encountered when hunting waterfowl. This degree of choke may also be desirable for some forms of trap shooting. At the other end of the spectrum, a very wide shot dispersion is desirable for short-range shooting situations such as skeet shooting.
The versatility provided by removable chokes does not come without certain tradeoffs. Modern choke tubes are threaded inserts, which are secured in shotgun barrel muzzles by using approximately 0.5 inches of very fine, continuous threads. The selection of this thread style is necessitated by the limited wall thickness available for this threaded connection, and the need for a secure installation. A certain amount of thread engagement is required to help ensure that the choke tube will not loosen extensively or be expelled from the barrel during firing. To this end, the choke tube is provided with continuous threads on its exterior surface. The barrel has a corresponding set of continuous threads located on its inner surface. Given this design configuration, a choke tube can require upwards of 20 revolutions to insert or extract. This process can be time-consuming and annoying for users.
Thus there is a need for a removable choke tube threaded insert that a user can more easily insert and extract using fewer revolutions, but that does not experience excessive loosening or expulsion during use.